Maintaining protection against invasive bacteria with protein–polysaccharide conjugate vaccines

Maintaining protection against invasive bacteria with protein–polysaccharide conjugate vaccines

Polysaccharide-encapsulated organisms are the leading cause of bacterial meningitis and pneumonia in children. The use of protein–polysaccharide conjugate vaccines in developed countries over the past two decades has markedly decreased the burden of disease and mortality from these organisms through direct protection of the immunized and through herd immunity. In the next decade, the widespread use of conjugate vaccines in the developing world should prevent millions of deaths. In this Science and Society article, we describe how vaccine-induced immunity wanes rapidly after vaccination in early childhood and argue that strategies that sustain protection in the population must be considered.

Types of Vaccines

Inactivated Vaccines

Inactivated vaccines are produced by killing the disease-causing microorganism with chemicals or heat. They cannot revert to the virulent, disease-causing, form. They often do not require refrigeration, which  makes them accessible to virtually everyone.  Inactivated vaccines can stimulate a relatively weak immune response and must be given more than once. Vaccines that require several doses or boosters can have a limited usefulness, especially for people who have limited access to regular health care. The flu shot, polio(ipv) hepatitis A are examples of inactivated vaccines.

Live, Attenuated Vaccines 

A live, attenuated vaccine,  is made by growing the disease-causing organism under special laboratory conditions that cause it to lose its virulence, or disease-causing attributes. Live vaccines require special handling and storage in order to maintain their potency. They produce antibody-mediated and cell-mediated immunity and require only one dose or booster. Most live vaccines are injected with the exception of oral polio (opv), oral Rotavirus (Rotateq), and flumist (flu) which is intranasal ( administered in the nose). The injected live vaccines are all components of the MMR( Measles, Mumps, Rubella), Chickenpox(Varicella), Shingles(Zostavax), and smallpox.
Live vaccines do have drawbacks. They can mutate and there is the possibility that the organism may revert to a virulent form and cause disease. People with compromised immune systems should not given live vaccines nor be around those who have recently received them due to possible vaccine shedding


A toxoid  is an inactivated toxin, which is a harmful substance produced by a microbe. Many microbes that infect people are not harmful. It is the toxins they produce that can cause illness. Tetanus is an example of this. The bacterium that causes tetanus can be found everywhere around us, but with plenty of oxygen, it is harmless. If, however, it is put into an environment without oxygen,  the organism changes and produces tetanus toxin. To inactivate such the toxins, the vaccines are treated with materials that cripple their disease-causing ability. Formalin, is often used to inactivate toxins and produce toxoids. Toxoid vaccines are used against tetanus and diphtheria.


Conjugate Vaccines 

For  conjugate vaccines, proteins or toxins from a second type of organism, one that an immature immune system can recognize, are linked to the outer coats of the disease-causing bacteria. This enables a young immune system to respond and defend against the disease agent.  The creation of an effective immunogen is most often used in bacterial polysaccharides for the prevention of invasive bacterial disease such as, Haemophilus influenzae type b (Hib), and Meningococcus, and Pneumococcal.


Subunit Vaccines

These vaccines contain purified antigens rather than whole organisms. The disadvantages of subunit vaccines are that the antibodies produced against the subunit may not recognize the same protein on the pathogen surface. Therefore, an isolated protein may not stimulate the immune system as well as a whole organism vaccine. The effectiveness of subunit vaccines is increased by adding adjuvants. Alum (aluminum salts) is a common adjuvant used in vaccines. Pertussis toxin, one of the components of the DTaP, acts as an adjuvant in that vaccine.  Subunit vaccines are used to protect against pneumonia caused by Streptococcus pneumoniae and against a type of meningitis.

Recombinant subunit vaccines like hepatitis B  is made by inserting a small portion of the hepatitis B virus’ genetic material into common baker’s yeast. This process induces the yeast to produce an antigen, which is thus purified. The purified antigen is then combined with an adjuvant.

Recombinant Vector Vaccines

A vaccine carrier, or vector, is a weakened virus or bacterium  which genetic material from another disease-causing organism can be inserted. The vaccinia virus is used to make recombinant vector vaccines such as smallpox. There are currently no recombinant vector vaccines are licensed for routine use in the United States.


DNA Vaccines

These vaccines use both the whole organism and its parts; the microbe’s genetic material. A DNA vaccine against a microbe could evoke a strong antibody response to the free-floating antigen secreted by cells, and would thus stimulate a strong cellular response against the microbial antigens displayed on cell surfaces. The DNA vaccine wouldn’t cause the disease since it doesn’t contain the microbe, just copies of a few of its genes. DNA vaccines being tested are influenza, bird flu, and herpes.


Immune Globulins

Immune globulins are made by collecting plasma from people who have contracted or were vaccinated for a particular disease, and their plasma contains protective antibodies, known as IgG.  These antibodies are isolated by fractionation of the plasma, purified and administered intravenously or by intramuscular injection, and thus providing an immediate protective effect. Immune globulins are used to generate an immediate protective immune response.